American Airlines has filed suit against Google for selling ads that show up in searches for American Airlines's trademarks. This is far from the first time Google has defended against such a suit, and I'm not aware of any keyword advertising case they've lost. Nevertheless, AA is determined to try, alleging direct, vicarious, and contributory trademark infringement. They also make an interesting (if uncompelling) argument that the “sponsored link” language above the ads falsely creates the impression that American Airlines itself sponsored or approves of the ads. (This is another example of a suit in which as users get more internet savvy, legal protections weaken, since AA's claims depend on the likelihood that users will be confused by the use of its trademarks.)
Where there's a profit, someone thinks they have a right to it; Google found a way to monetize internet searches, so now trademark holders want the exclusive right to profit off of searches of their trademarks. This is a misreading of what trademark is meant to do. Trademark law exists to protect consumers: trademarks are used to identify the source of goods and services, so consumers can trust that the can labeled “Dr Pepper” really does contain that delicious nectar and not some pale, bitter imitation. Companies who own trademarks, however, want to turn it into some sort of personal right to control any mention of their products. It's clear how this case should turn out, but both American Airlines and Google have the resources to fight it to the bitter end, so this could turn into an interesting showdown.